Compared to the formalism described above and used in [1]}, [2]}, [3]}, some adjustments are necessary to the
SHERPA resummation framework. In particular we have to take into
account the fact that
the angularities are sensitive to radiation within the hardest jet in the
event only.
Let us label, for definiteness, the initial state legs as \(l=1,2\)  and the measured
final state leg as \(l=3\) . As our observable is not sensitive to radiation
collinear to the initial state legs, we are allowed to set \(\mathcal {P}=1\) 
and \(R_1=R_2=0\)  in Eq. (REF ).
Keeping in mind that the Born phase space is given by final states
consisting of a single parton plus the \(Z\)  boson, only one radiator is
left. In terms of Eq. (REF ), the angularity
observables \(\lambda ^1_\alpha \)  can be parametrised by

a = 1 ,
